The present invention relates to a guide bar for a chain saw of the type used, for example, for cutting down or trimming trees and, in particular, to a guide bar that incorporates a chain-tightening device which enables a user to readily and easily adjust the tightness of the saw chain.
Generally, when a chain saw is employed for a long period of time, the saw chain is caused to elongate due to the abrasion of the portions of the saw chain that engage the guide bar, thus loosening the saw chain and sometimes allowing disengagement of the saw chain from the driving chain sprocket wheel or the guide bar. Therefore, the saw chain is required to be re-tightened occasionally. Further, it is also required at the occasion of exchanging the saw chain for a new one to adjust the tightness of the new saw chain after the new saw chain is mounted on the driving chain sprocket wheel and guide bar.
Chain-tightening devices for adjusting the tightness of the saw chain have been conventionally provided on the main body and side guard of the chain saw. Examples of such a chain-tightening devices are described and shown in Japanese Utility Model Unexamined Publication S61-93201 and Japanese Patent Unexamined Publication H7-314402.
It is required, for the provision of the conventional chain-tightening device, to separately attach accessories to the main body and side guard of the chain saw and to configure the main body and side guard for mounting the chain-tightening device on the chain saw, thus making the chain saw complicated in construction, increasing the number of parts required for the provision of the chain-tightening device, and adding to the costs for manufacturing the chain saw. In addition, the maintenance and inspection of the chain-tightening device can be troublesome, and the chain-tightening device cannot be attached to an existing chain saw.
Additionally, since the conventional chain-tightening device is generally mounted on the main body and side guard of the chain saw, the tightening of the chain is required to be conducted by turning adjustment screws attached to the chain-tightening device using a tool such as a screwdriver. In this case, the adjustment screws are inevitably mounted close to one side wall of the main body of chain saw (generally, the right side wall as viewed from the proximal end of the chain saw), so that the operator is required, for the purpose of turning the adjustment screws, to manipulate a tool such as a screwdriver by directing it in the longitudinal direction of the main body of chain saw, in the direction perpendicular to the main body of chain saw, or in an intermediate direction thereof (or in an oblique direction) so as to position the tool to engage with the adjustment screw members. This often means that the operability for adjusting the tightness of saw chain is inferior and at the same time, it is difficult to confirm the degree of tightness of the saw chain while turning the adjustment screw members, thus making the adjustment of the chain tension rather difficult.